Network Working Group Mustapha Aissaoui
Internet Draft Peter Busschbach
Expires: October 2009 Alcatel-Lucent
Dave Allan
Nortel
Monique Morrow
Luca Martini
Cisco Systems Inc.
Thomas Nadeau
BT
Yaakov Stein
RAD Data Communications
Editors
April 15, 2009
Pseudo Wire (PW) OAM Message Mapping
draft-ietf-pwe3-oam-msg-map-10.txt
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Copyright and License Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
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Abstract
This document specifies the mapping and notification of defect states
between a Pseudo Wire and the Attachment Circuits (AC) of the end-to-
end emulated service. This document covers the case whereby the ACs
and the PWs are of the same type in accordance to the PWE3
architecture [RFC3985] such that a homogenous PW service can be
constructed.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119.
Table of Contents
1. Acknowledgments................................................4
2. Contributors...................................................4
3. Introduction...................................................5
4. Terminology....................................................5
5. Reference Model and Defect Locations...........................7
6. Abstract Defect States.........................................8
7. OAM Models....................................................10
8. PW Defect States and Defect Notifications.....................12
8.1. PW Defect Notification Mechanisms........................12
8.1.1. LDP Status TLV......................................13
8.1.2. L2TP Circuit Status AVP.............................14
8.1.3. BFD Diagnostic Codes................................16
8.2. PW Defect State Entry/Exit...............................18
8.2.1. PW receive defect state entry/exit criteria.........18
8.2.2. PW transmit defect state entry/exit criteria........19
9. Procedures for ATM PW Service.................................19
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9.1. AC receive defect state entry/exit criteria..............19
9.2. AC transmit defect state entry/exit criteria.............20
9.3. Consequent Actions.......................................21
9.3.1. PW receive defect state entry/exit..................21
9.3.2. PW transmit defect state entry/exit.................22
9.3.3. PW defect state in ATM Port Mode PW Service.........22
9.3.4. AC receive defect state entry/exit..................22
9.3.5. AC transmit defect state entry/exit.................24
10. Procedures for Frame Relay PW Service........................24
10.1. AC receive defect state entry/exit criteria.............24
10.2. AC transmit defect state entry/exit criteria............24
10.3. Consequent Actions......................................25
10.3.1. PW receive defect state entry/exit.................25
10.3.2. PW transmit defect state entry/exit................25
10.3.3. PW defect state in the FR Port Mode PW service.....26
10.3.4. AC receive defect state entry/exit.................26
10.3.5. AC transmit defect state entry/exit................26
11. Procedures for TDM PW Service................................26
11.1. AC receive defect state entry/exit criteria.............27
11.2. AC transmit defect state entry/exit criteria............27
11.3. Consequent Actions......................................28
11.3.1. PW receive defect state entry/exit.................28
11.3.2. PW transmit defect state entry/exit................28
11.3.3. AC receive defect state entry/exit.................28
12. Procedures for CEP PW Service................................29
12.1. Defect states...........................................30
12.1.1. PW receive defect state entry/exit criteria........30
12.1.2. PW transmit defect state entry/exit criteria.......30
12.1.3. AC receive defect state entry/exit criteria........30
12.1.4. AC transmit defect state entry/exit criteria.......30
12.2. Consequent actions......................................31
12.2.1. PW receive defect state entry/exit.................31
12.2.2. PW transmit defect state entry/exit................31
12.2.3. AC receive defect state entry/exit.................31
13. Security Considerations......................................32
14. IANA Considerations..........................................32
15. References...................................................32
15.1. Normative References....................................32
15.2. Informative References..................................33
16. Editor's Addresses...........................................34
Informative Appendix A: Native Service Management................35
- Frame Relay Management.....................................35
- ATM Management.............................................36
Informative Appendix B: PW Defects and Detection tools...........37
- PW Defects.................................................37
- Packet Loss.............................................38
- PW Defect Detection Tools..................................38
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1. Acknowledgments
The editors would like to acknowledge the important contributions of
Hari Rakotoranto, Eric Rosen, Mark Townsley, Michel Khouderchah,
Bertrand Duvivier, Vanson Lim, Chris Metz, Ben Washam, Tiberiu
Grigoriu, Neil McGill, and Amir Maleki.
2. Contributors
Thomas D. Nadeau, tom.nadeau@bt.com
Monique Morrow, mmorrow@cisco.com
Peter B. Busschbach, busschbach@alcatel-lucent.com
Mustapha Aissaoui, mustapha.aissaoui@alcatel-lucent.com
Matthew Bocci, matthew.bocci@alcatel-lucent.co.uk
David Watkinson, david.watkinson@alcatel-lucent.com
Yuichi Ikejiri, y.ikejiri@ntt.com
Kenji Kumaki, kekumaki@kddi.com
Satoru Matsushima, satoru@ft.solteria.net
David Allan, dallan@nortel.com
Himanshu Shah, hshah@ciena.com
Simon Delord, sdelord@uecomm.com.au
Vasile Radoaca, vasile.radoaca@alcatel-lucent.com
Carlos Pignataro, cpignata@cisco.com
Luca Martini, lmartini@cisco.com
Yaakov (J) Stein, yaakov_s@rad.com
Teruyuki Oya, teruyuki.oya@tm.softbank.co.jp
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3. Introduction
This document specifies the mapping and notification of defect states
between a Pseudo Wire and the Attachment Circuits (AC) of the end-
to-end emulated service. It covers the case whereby the ACs and the
PWs are of the same type in accordance to the PWE3 architecture
[RFC3985] such that a homogeneous PW service can be constructed.
This document is motivated by the requirements put forth in [RFC4377]
and [RFC3916]. Its objective is to standardize the behavior of PEs
with respects to failures on PWs and ACs, so that there is no
ambiguity about the alarms generated and consequent actions
undertaken by PEs in response to specific failure conditions.
This document covers PWE over MPLS PSN, PWE over MPLS-IP PSN and PWE
over L2TP-IP PSN.
The Ethernet PW service is covered in a separate document [ETH-OAM-
IWK].
4. Terminology
AIS Alarm Indication Signal
AC Attachment circuit
BDI Backward Defect Indication
CC Continuity Check
CE Customer Edge
CPCS Common Part Convergence Sub-layer
DLC Data Link Connection
FDI Forward Defect Indication
FRBS Frame Relay Bearer Service
IWF Interworking Function
LB Loopback
NE Network Element
NS Native Service
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OAM Operations and Maintenance
PE Provider Edge
PW Pseudowire
PSN Packet Switched Network
RDI Remote Defect Indication
SDU Service Data Unit
VCC Virtual Channel Connection
VPC Virtual Path Connection
The rest of this document will follow the following conventions.
The words "defect" and "fault" are used inter-changeably to mean a
condition which causes user packets not to be forwarded between the
CE endpoints of the PW service.
The words "defect notification" and "defect indication" are used
inter-changeably to mean an OAM message generated by a PE and sent to
other nodes in the network to convey the defect state local to this
PE.
The PW can ride over three types of Packet Switched Network (PSN). A
PSN which makes use of LSPs as the tunneling technology to forward
the PW packets will be referred to as an MPLS PSN. A PSN which makes
use of MPLS-in-IP tunneling [RFC4023], with an MPLS shim header used
as PW demultiplexer, will be referred to as an MPLS-IP PSN. A PSN
which makes use of L2TPv3 [RFC3931] as the tunneling technology with
the L2TPv3 Session ID as the PW demultiplexer will be referred to as
L2TP-IP PSN.
If LSP-Ping [RFC4379] is run over a PW as described in [RFC4377], it
will be referred to as VCCV-Ping.
If BFD is run over a PW as described in [RFC4377], it will be
referred to as VCCV-BFD [VCCV-BFD].
In the context of this document a PE forwards packets between an AC
and a PW. The other PE that terminates the PW is the peer PE or
remote PE and the attachment circuit associated with the far-end PW
termination is the remote AC.
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Defects are discussed in the context of defect states, and the
criteria to enter and exit the defect state. The direction of defects
is discussed from the perspective of the observing PE.
A receive defect is one that impacts information transfer to the
observing PE. It impacts the observing PEs ability to receive
information.
A transmit defect is one that uniquely impacts information sent or
relayed by the observing PE.
A receive defect generally also impacts information sent or relayed
by the observing PE. Therefore the receive defect state is considered
to be a superset of the two defect states. Thus, when a PE enters
both receive and transmit defect states related to the same PW
service, the receive defect takes precedence over the transmit defect
in terms of the consequent actions.
A forward defect indication is sent in the same direction as the user
traffic impacted by the defect. A reverse defect indication is sent
in the opposite direction of the traffic impacted by the defect.
5. Reference Model and Defect Locations
Figure 1 illustrates the PWE3 network reference model with an
indication of the possible defect locations. This model will be
referenced in the remainder of this document for describing the OAM
procedures.
ACs PSN tunnel ACs
+----+ +----+
+----+ | PE1|==================| PE2| +----+
| |---(a)---(b)..(c)......PW1..(d)..(c)..(f)---(e)---| |
| CE1| (N1) | | | | (N2) |CE2 |
| |----------|............PW2.............|----------| |
+----+ | |==================| | +----+
^ +----+ +----+ ^
| Provider Edge 1 Provider Edge 2 |
| |
|<-------------- Emulated Service ---------------->|
Customer Customer
Edge 1 Edge 2
Figure 1: PWE3 Network Defect Locations
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In all interworking scenarios described in this document, it is
assumed the AC and the PW are of the same type at PE1. The procedures
described in this document apply to PE1. PE2 implements the identical
functionality for a homogeneous service (although it is not required
to as long as the notifications across the PWs are consistent).
The following is a brief description of the defect locations:
a. Defect in the first native service network (N1). This covers
any defect in the N1 which impacts all or a subset of ACs
terminating in PE1. The defect is conveyed to PE1 and to the
remote native service network (N2) using the native service
specific OAM defect indication.
b. Defect on a PE1 AC interface.
c. Defect on a PE1 PSN interface.
d. Defect in the PSN network. This covers any defect in the PSN
which impacts all or a subset of PWs terminating in a PE. The
defect is conveyed to the PE using a PSN and/or a PW specific
OAM defect indication. Note that both data plane defects and
control plane defects must be taken into consideration. Even
though control messages may follow a different path than the
PW data plane traffic, a control plane failure may affect the
PW status.
e. Defect in the second native service network (N2). This covers
any defect in N2 which impacts all or a subset of ACs
terminating in PE2 (which is considered a remote AC defect in
the context of procedures outlined in this draft). The defect
is conveyed to PE2 and to the remote native service network
(N1) using the native service OAM defect indication.
f. Defect on a PE2 AC interface (which is also considered a
remote AC defect in the context of this draft).
6. Abstract Defect States
PE1 must track four defect states that reflect the observed states of
both directions of the PW service on both the AC and the PW sides.
Defects may impact one or both directions of the PW service.
The observed state is a combination of defects directly detected by
PE1 and defects it has been made aware of via notifications.
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+-----+
----AC receive---->| |-----PW transmit---->
CE1 | PE1 | PE2/CE2
<---AC transmit-----| |<----PW receive-----
+-----+
(arrows indicate direction of user traffic impacted by a defect)
Figure 2: Receive and Transmit Defect States
PE1 will directly detect or be notified of AC receive or PW receive
defects as they occur upstream of PE1 and impact traffic being sent
to PE1. As a result, PE1 enters the AC or PW receive defect state.
In Figure 2, PE1 may be notified of a receive defect in the AC by
receiving a Forward Defect indication, e.g., ATM AIS, from an ATM
switch in network N1. This defect notification indicates that user
traffic sent by CE1 may not be received by PE1 due to a defect. PE1
can also directly detect an AC receive defect if it resulted from a
failure of the receive side in the local port or link over which the
AC is configured.
Similarly, PE1 may detect or be notified of a receive defect in the
PW by receiving a Forward Defect indication from PE2. If PW status is
used for fault notification, this message will indicate a Local PSN-
facing PW (egress) Transmit Fault or a Local Attachment Circuit
(ingress) Receive Fault at PE2, as described in Section 8.1.1. . This
defect notification indicates that user traffic sent by CE2 may not
be received by PE1 due to a defect. As a result, PE1 enters the PW
receive defect state.
Note that a Forward Defect indication is sent in the same direction
as the user traffic impacted by the defect.
Generally, a PE cannot detect transmit defects directly and will
therefore need to be notified of AC transmit or PW transmit defects
by other devices.
In Figure 2, PE1 may be notified of a transmit defect in the AC by
receiving a Reverse Defect indication, e.g., ATM RDI, from CE1. This
defect relates to the traffic sent by PE1 to CE1 on the AC.
Similarly, PE1 may be notified of a transmit defect in the PW by
receiving a Reverse Defect indication from PE2. If PW status is used
for fault notification, this message will indicate a Local PSN-facing
PW (ingress) Receive Fault or a Local Attachment Circuit (egress)
Transmit Fault at PE2, as described in Section 8.1.1. . This defect
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impacts the traffic sent by PE1 to CE2. As a result, PE1 enters the
PW transmit defect state.
Note that a Reverse Defect indication is sent in the reverse
direction to the user traffic impacted by the defect.
The procedures outlined in this document define the entry and exit
criteria for each of the four states with respect to the set of PW
services within the document scope and the consequent actions that
PE1 must perform.
When a PE enters both receive and transmit defect states related to
the same PW service, then the receive defect takes precedence over
transmit defect in terms of the consequent actions.
7. OAM Models
A homogeneous PW service forwards packets between an AC and a PW of
the same type. It thus implements both a Native Service OAM
mechanism and a PW OAM mechanism. PW OAM defect notification
messages are described in Section 8.1. Native Service (NS) OAM
messages are described in Appendix A.
This document defines two different modes for operating OAM on a PW
service which dictate the mapping between the NS OAM the PW OAM
defect notification messages.
The first one operates a single emulated OAM loop end-to-end between
the endpoints of the PW service. This is referred to as "single
emulated OAM loop" mode and is illustrated in Figure 3.
|<----- AC ----->|<----- PW ----->|<----- AC ----->|
| | | |
___ ===============_
|CE|---=NS-OAM=>---(---=NS-OAM=>---)---=NS-OAM=>---|CE|
=============== /
\ /
---=PW-OAM=>---
Figure 3: Single Emulated OAM Loop mode
This mode implements the following behavior. We use the words
upstream and downstream to identify PEs in relation to a specific
traffic direction.
a. An upstream PE node MUST transparently relay NS OAM messages
over the PW.
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b. An upstream PE node MUST signal local failures affecting the
AC using a NS defect notification OAM message sent over the
PW. In the case that it is not possible to generate NS OAM
messages (e.g. because the defect interferes with NS OAM
message generation) the PE MUST signal local failures
affecting the AC using a PW defect notification OAM message.
c. An upstream PE node MUST signal local failures affecting the
PW using a PW defect notification OAM message.
d. A downstream PE node MUST insert a NS defect notification OAM
message into the AC when it detects or is notified of a
defect in the PW or remote AC. This includes receiving a PW
defect notification message and translating it into a NS
defect notification OAM message over the AC. The latter is
required for handling defects signaled by a peer PE with PW
OAM messaging.
The "single emulated OAM loop" mode is suitable for PW services
which have a widely deployed NS OAM mechanism that operates within
the AC. This document specifies the use of this mode for ATM PW, TDM
PW, and CEP PW services. It is the default mode of operation for all
ATM cell-mode PW services and the only mode specified for TDM and
CEP PW services. It is optional for AAL5 PDU transport and AAL5 SDU
transport modes.
The second mode operates three OAM loops which join at the AC/PW
boundary of a PE. This is referred to as "coupled OAM loops" mode
and is illustrated in Figure 4.
|<----- AC ----->|<----- PW ----->|<----- AC ----->|
| | | |
__ ===============__
|CE|---=NS-OAM=>---(---------------)---=NS-OAM=>---|CE|
\ =============== /
\ /
\ /
-------=PW-OAM=>------
Figure 4: Coupled OAM Loops mode
This mode implements the following behavior. We use the words
upstream and downstream to identify PEs in relation to a specific
traffic direction.
a. An upstream PE node MUST terminate and translate a received
NS defect notification OAM message to a PW defect
notification message.
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b. An upstream PE node MUST signal local failures affecting the
AC using a PW defect notification OAM message to the remote
PE.
c. An upstream PE node MUST signal local failures affecting the
PW using a PW defect notification OAM message.
d. A downstream PE node MUST insert a NS defect notification OAM
message into the AC when it detects or is notified of a
defect in the PW or remote AC. This includes support
receiving a PW defect notification message and translating it
into a NS defect notification OAM message over the AC.
This document specifies the "coupled OAM loops" mode as the default
mode for a FR PW service and for ATM AAL5 PDU transport and AAL5 SDU
transport services and as optional for ATM VCC cell mode services.
It does not specify the use of this mode for TDM PW, CEP PW, and ATM
VPC cell mode PW services. In the latter last case, a PE node must
pass transparently VC-level (F5) ATM OAM cells over the PW while
terminating and translating VP-level (F4) OAM cells. Thus, it cannot
operate a pure "coupled OAM loops" mode.
8. PW Defect States and Defect Notifications
8.1. PW Defect Notification Mechanisms
For a MPLS PSN and a MPLS-IP PSN, a PE node which establishes a PW
using LDP SHALL use LDP status TLV as the mechanism for AC and PW
status and defect notification [RFC4447]. Additionally, a PE node MAY
use VCCV-BFD Connectivity Verification (CV) types for fault detection
only but SHOULD notify the remote PE using LDP Status TLV. These CV
types are 0x04 and 0x10 [VCCV-BFD].
A PE node which establishes a PW using other means than LDP, e.g.,
static configuration, MAY use VCCV-BFD CV types for AC and PW status
and defect notification. These CV types are 0x08 and 0x20 [VCCV-BFD].
These CV types SHOULD NOT be used when the PW is established with the
LDP control plane.
For a L2TP-IP PSN, A PE node SHOULD use the Circuit Status AVP as the
mechanism for AC and PW status and defect notification. In its most
basic form, the Circuit Status AVP [RFC3931] in a Set-Link-Info (SLI)
message can signal active/inactive AC status. The Circuit Status AVP
is proposed to be extended to convey status and defects in the AC and
the PSN-facing PW in both ingress and egress directions, i.e., four
independent status bits without the need to tear down the sessions or
control connection [L2TP-Status].
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When a PE does not support the Circuit Status AVP, it MAY use the
StopCCN and the CDN message to bring down L2TP sessions in a similar
way LDP uses the Label Withdrawal to bring down a PW. A PE node may
use the StopCCN to shutdown the L2TP control connection, and
implicitly all L2TP sessions associated with that control connection
without any explicit session control messages. This is in the case of
a failure which impacts all L2TP sessions, i.e., all PWs, managed by
the control connection. It may use the CDN message to disconnect a
specific L2TP session when a failure affects a specific PW.
Additionally, a PE node MAY use VCCV-BFD CV types 0x04 and 0x10 for
fault detection only but SHOULD notify the remote PE using the
Circuit Status AVP. A PE node which establishes a PW using other
means than L2TP control plane MAY use VCCV-BFD CV types 0x08 and 0x20
for AC and PW status and defect notification. These CV types SHOULD
NOT be used when the PW is established with the L2TP control plane.
8.1.1. LDP Status TLV
[RFC4446] defines the following PW status code points:
0x00000000 - Pseudo Wire forwarding (clear all failures)
0x00000001 - Pseudo Wire Not Forwarding
0x00000002 - Local Attachment Circuit (ingress) Receive Fault
0x00000004 - Local Attachment Circuit (egress) Transmit Fault
0x00000008 - Local PSN-facing PW (ingress) Receive Fault
0x00000010 - Local PSN-facing PW (egress) Transmit Fault
[RFC4447] specifies that "Pseudo Wire forwarding" code point is used
to clear all faults. It also specifies that "Pseudo Wire Not
Forwarding" code is used to convey any other defect that cannot be
represented by the other code points.
The code points used in the LDP status TLV in a PW status
notification message convey the defect view of the originating PE.
The originating PE conveys this state in the form of a forward defect
or a reverse defect indication.
The forward and reverse defect indication definitions used in this
document map to the LDP Status TLV codes as follows:
Forward defect indication - corresponds to the logical OR of
Local Attachment Circuit (ingress) Receive Fault,
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Local PSN-facing PW (egress) Transmit Fault, and
PW not Forwarding Fault
Reverse defect indication - corresponds to the logical OR of
Local Attachment Circuit (egress) Transmit Fault and
Local PSN-facing PW (ingress) Receive Fault
A PE SHALL thus use PW status notification messages to report all
failures affecting the PW service including, but not restricted, to
the following:
- Failures detected through defect detection mechanisms in
the MPLS and MPLS-IP PSN
- Failures detected through VCCV-Ping or VCCV-BFD CV types
0x04 and 0x10 for fault detection only
- Failures within the PE that result in an inability to
forward traffic between the AC and the PW
- Failures of the AC or in the L2 network affecting the AC
as per the rules detailed in Section 7. for the "single
emulated OAM loop" mode and "coupled OAM loops" mode.
Note that there are two situations which require PW label withdrawal
as opposed to a PW status notification by the PE. The first one is
when the PW is taken administratively down in accordance to
[RFC4447]. The second one is when the Target LDP session established
between the two PEs is lost. In the latter case, the PW labels will
need to be re-signaled when the Targeted LDP session is re-
established.
8.1.2. L2TP Circuit Status AVP
[RFC3931] defines the Circuit Status AVP in the Set-Link-Info (SLI)
message to exchange initial status and status changes in the circuit
to which the pseudowire is bound. [L2TP-Status] defines extensions to
the Circuit Status AVP that are analogous to the PW Status TLV
defined for LDP. Consequently, for L2TP-IP, the Circuit Status AVP
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is used in the same fashion as the PW Status described in the
previous section.
If the extended Circuit Status bits are not supported, and instead
only the "A-bit" (Active) is used as described in [RFC3931], a PE MAY
use CDN messages to clear L2TPv3 sessions in the presence of session-
level failures detected in the L2TP-IP PSN.
A PE MUST set the Active bit in the Circuit Status to clear all
faults, and it MUST clear the Active bit in the Circuit Status to
convey any defect that cannot be represented explicitly with specific
Circuit Status flags from [RFC3931] or [L2TP-Status].
The forward and reverse defect indication definitions used in this
document map to the L2TP Circuit Status AVP as follows:
Forward defect indication - corresponds to the logical OR of
Local Attachment Circuit (ingress) Receive Fault,
Local PSN-facing PW (egress) Transmit Fault, and
PW not Forwarding Fault
Reverse defect indication- corresponds to the logical OR of
Local Attachment Circuit (egress) Transmit Fault and
Local PSN-facing PW (ingress) Receive Fault
The status notification conveys the defect view of the originating
LCCE (PE).
When the extended Circuit Status definition of [L2TP-Status] is
supported, a PE SHALL use the Circuit Status to report all failures
affecting the PW service including, but not restricted, to the
following:
- Failures detected through defect detection mechanisms in
the L2TP-IP PSN.
- Failures detected through VCCV-Ping or VCCV-BFD CV types
0x04 and 0x10 for fault detection only
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- Failures within the PE that result in an inability to
forward traffic between the AC and the PW
- Failures of the AC or in the L2 network affecting the AC
as per the rules detailed in Section 7. for the "single
emulated OAM loop" mode and the "coupled OAM loops" mode.
When the extended Circuit Status definition of [L2TP-Status] is not
supported, a PE SHALL use the A-bit in the Circuit Status AVP in SLI
to report:
- Failures of the AC or in the L2 network affecting the AC
as per the rules detailed in Section 7. for the "single
emulated OAM loop" mode and the "coupled OAM loops" mode.
When the extended Circuit Status definition of [L2TP-Status] is not
supported, a PE MAY use the CDN and StopCCN messages in a similar way
to an MPLS PW label withdrawal to report:
- Failures detected through defect detection mechanisms in
the L2TP-IP PSN (using StopCCN)
- Failures detected through VCCV (pseudowire level) (using
CDN)
- Failures within the PE that result in an inability to
forward traffic between ACs and PW (using CDN)
For ATM L2TPv3 pseudowires, in addition to the Circuit Status AVP, a
PE MAY use the ATM Alarm Status AVP [RFC4454] to indicate the reason
for the ATM circuit status and the specific alarm type, if any. This
AVP is sent in the SLI message to indicate additional information
about the ATM circuit status.
L2TP control connections use Hello messages as a keep-alive facility.
It is important to note that if a PSN failure is such that the loss
of connectivity is detected when it triggers a keep-alive timeouts,
the control connection is cleared. L2TP Hello messages are sent in-
band with the data plane, with respect to the source and destination
addresses, IP protocol number and UDP port (when UDP is used).
8.1.3. BFD Diagnostic Codes
[BFD] defines a set of diagnostic codes that partially overlap with
failures that can be communicated through LDP Status TLV or L2TP
Circuit Status AVP. This section describes the behavior of the PE
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nodes with respect to using one or both methods for detecting and
propagating defect state.
For a MPLS-PSN, the PEs negotiate the use of the VCCV capabilities
when the label mapping messages are exchanged to establish the two
directions of the PW. An OAM capability TLV is signaled as part of
the PW FEC interface parameters TLV. For L2TP-IP PSNs, the PEs
negotiate the use of VCCV during the pseudowire session
initialization using the VCCV AVP [RFC5085].
The CV Type Indicators field in this TLV defines a bitmask used to
indicate the specific OAM capabilities that the PE can make use of
over the PW being established.
A CV type of 0x04 or 0x10 indicates that BFD is used for PW fault
detection only [VCCV-BFD]. These CV types MAY be used any time the PW
is established using LDP or L2TP control planes.
In this mode, only the following diagnostic (Diag) codes specified in
[BFD] will be used, they are:
0 - No diagnostic
1 - Control detection time expired
7 - Administratively Down
A PE MUST use code 0 to indicate to its peer PE that is correctly
receiving BFD control messages. It MUST use the second code to
indicate that to its peer it has stopped receiving BFD control
messages. A PE shall use "Administrative down" to bring down the BFD
session when the PW is brought down administratively. All other
defects, such as AC/PW defects and PE internal failures that prevent
it from forwarding traffic, MUST be communicated through LDP Status
TLV in the case of MPLS PSN or MPLS-IP PSN, or through the
appropriate L2TP codes in the Circuit Status AVP in the case of L2TP-
IP PSN.
A CV type of 0x08 or 0x20 in the OAM capabilities TLV indicates that
BFD is used for both PW fault detection and Fault Notification. In
addition to the above diagnostic codes, a PE used the following codes
to signal AC defects and other defects impacting forwarding over the
PW service:
6 -- Concatenated Path Down
8 -- Reverse Concatenated Path Down
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TBD -- PW not forwarding
A PE MAY use the "PW not forwarding" code to convey any other defect
that cannot be represented by code points 6 and 8. In general, this
applies to a defect that does not cause the PW to be torn down. This
implies the BFD session must not be brought down when this defect
exists.
The forward and reverse defect indication definitions used in this
document map to the BFD codes as follows:
Forward defect indication - corresponds to the logical OR of
Concatenated Path Down and PW not forwarding
Reverse defect indication- corresponds to Reverse
Concatenated Path Down
These diagnostic codes are used to signal receive and reverse defect
states respectively when the PEs negotiated the use of BFD as the
mechanism for AC and PW fault detection and status signaling
notification. As stated in Section 8.1. , these CV types SHOULD NOT
be used when the PW is established with the LDP or L2TP control
plane.
8.2. PW Defect State Entry/Exit
8.2.1. PW receive defect state entry/exit criteria
PE1 will enter the PW receive defect state if one or more of the
following occurs:
- It receives a forward defect indication from PE2, which
indicates PE2 detected or was notified of a PW fault
downstream of it or that there was a receive defect on
remote AC.
- It detects loss of connectivity on the PSN tunnel
upstream of PE1 which affects the traffic it receives
from PE2.
- It detects a loss of PW connectivity through VCCV-BFD or
VCCV-PING which affects the traffic it receives from PE2.
Note that if the PW control session between the PEs fails, the PW is
torn down and needs to be re-established. This includes failure of
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the T-LDP session, the L2TP session, or the L2TP control connection.
However, the consequent actions towards the ACs are the same as if
the PW entered the receive defect state.
PE1 will exit the PW receive defect state when the following
conditions are true. Note that this may result in a transition to the
PW operational state or the PW transmit defect state.
- All defects it had previously detected have disappeared,
and
- PE2 cleared the forward defect indication if applicable.
8.2.2. PW transmit defect state entry/exit criteria
PE1 will enter the PW transmit defect state if the following
conditions are true:
- it receives a reverse defect indication from PE2 which
indicates that PE2 detected or was notified of a PW fault
upstream of it or that there was a transmit fault on the
remote AC, and
- it is not already in the PW receive defect state.
PE1 will exit the transmit defect state if it receives an OAM message
from PE2 clearing the reverse defect indication, or it has entered
the PW receive defect state.
For a PWE3 over a L2TP-IP PSN using the basic Circuit Status AVP
[RFC3931], the PW transmit defect state is not valid and a PE can
only enter the PW receive defect state.
9. Procedures for ATM PW Service
9.1. AC receive defect state entry/exit criteria
When operating in the "coupled OAM loops" mode, PE1 enters the AC
receive defect state if any of the following conditions are met:
a. It detects or is notified of a physical layer fault on
the ATM interface.
b. It receives an end-to-end F4 AIS OAM flow on a VP AC,
or an end-to-end F5 AIS OAM flow on a VC AC,
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indicating that the ATM VPC or VCC is down in the
adjacent L2 ATM network.
c. It receives a segment F4 AIS OAM flow on a VP AC, or a
segment F5 AIS OAM flow on a VC AC, provided that the
operator has provisioned segment OAM and the PE is not
a segment end-point
d. It detects loss of connectivity on the ATM VPC/VCC
while terminating segment or end-to-end ATM continuity
check (ATM CC) cells with the local ATM network and
CE.
When operating in the "coupled OAM loops" mode, PE1 exits the AC
Receive defect state when all defects it had previously detected have
disappeared.
When operating in the "single emulated OAM loop" mode, PE1 enters the
AC receive defect state if any of the following conditions are met:
a. It detects or is notified of a physical layer fault on
the ATM interface.
b. It detects loss of connectivity on the ATM VPC/VCC
while terminating segment ATM continuity check (ATM
CC) cells with the local ATM network and CE.
When operating in the "single emulated OAM loop" mode, PE1 exits the
AC receive defect state when all defects it had previously detected
have disappeared.
The exact conditions under which a PE enters and exits the AIS state,
or declares that connectivity is restored via ATM CC are defined in
Section 9.2 of ITU-T Recommendation I.610 [ITU-T I.610].
9.2. AC transmit defect state entry/exit criteria
When operating in the coupled-loop mode, PE1 enters the AC transmit
defect state if any of the following conditions are met:
a. It terminates an end-to-end F4 RDI OAM flow, in the
case of a VPC, or an end-to-end F5 RDI OAM flow, in
the case of a VCC, indicating that the ATM VPC or VCC
is down in the adjacent L2 ATM.
b. It receives a segment F4 RDI OAM flow on a VP AC, or a
segment F5 RDI OAM flow on a VC AC, provided that the
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operator has provisioned segment OAM and the PE is not
a segment end-point
PE1 exits the AC transmit defect state if the AC state transitions to
working or to the AC receive defect state. The exact conditions for
exiting the RDI state are described in Section 9.2 of ITU-T
Recommendation I.610 [ITU-T I.610].
Note that the AC transmit defect state is not valid when operating in
the "single emulated OAM loop" mode as PE1 transparently forwards the
received RDI cells as user cells over the ATM PW to the remote CE.
9.3. Consequent Actions
In the reminder of this section, the text refers to AIS, RDI and CC
without specifying whether it is an F4 (VP-level) flow or an F5 (VC-
level) flow, or whether it is an end-to-end or a segment flow.
Precise ATM OAM procedures for each type of flow are specified in
Section 9.2 of ITU-T Recommendation I.610 [ITU-T I.610].
9.3.1. PW receive defect state entry/exit
On entry to the PW receive defect state:
a. PE1 MUST commence AIS insertion into the corresponding
AC.
b. PE1 MUST cease generation of CC cells on the
corresponding AC, if applicable.
c. If the PW failure was detected by PE1 without
receiving a forward defect indication from PE2, PE1
MUST assume PE2 has no knowledge of the defect and
MUST notify PE2 in the form of a reverse defect
indication.
On exit from the PW receive defect state:
a. PE1 MUST cease AIS insertion into the corresponding
AC.
b. PE1 MUST resume any CC cell generation on the
corresponding AC, if applicable.
c. PE1 MUST clear the reverse defect indication to PE2 if
applicable.
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9.3.2. PW transmit defect state entry/exit
On entry to the PW Transmit Defect State:
a. PE1 MUST commence RDI insertion into the corresponding
AC.
b. If the PW failure was detected by PE1 without
receiving a reverse defect indication from PE2, PE1
MUST assume PE2 has no knowledge of the defect and
MUST notify PE2 in the form of a forward defect
indication.
On exit from the PW Transmit Defect State:
a. PE1 MUST cease RDI insertion into the corresponding
AC.
b. PE1 MUST clear the forward defect indication to PE2 if
applicable.
9.3.3. PW defect state in ATM Port Mode PW Service
In case of transparent cell transport PW service, i.e., "port mode",
where the PE does not keep track of the status of individual ATM VPCs
or VCCs, a PE cannot relay PW defect state over these VCCs and VPCs.
If ATM CC is run on the VCCs and VPCs end-to-end (CE1 to CE2), or on
a segment originating and terminating in the ATM network and spanning
the PSN network, it will timeout and cause the CE or ATM switch to
enter the ATM AIS state.
9.3.4. AC receive defect state entry/exit
On entry to the AC receive defect state and when operating in the
"coupled OAM loops" mode:
a. PE1 MUST send a forward defect indication to PE2.
b. PE1 MUST commence insertion of ATM RDI cells into the
AC towards CE1.
When operating in the "single emulated OAM loop" mode, PE1 must be
able to support two options, subject to the operator's preference.
The default option is the following:
On entry to the AC receive defect state:
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a. PE1 MUST transparently relay ATM AIS cells, or, in the
case of a local AC defect, commence insertion of ATM
AIS cells into the corresponding PW towards CE2.
b. If the defect interferes with NS OAM message
generation, PE1 MUST send a forward defect indication
to PE2.
c. PE1 MUST cease the generation of CC cells on the
corresponding PW, if applicable.
In certain operational models, for example in the case that the ATM
access network is owned by a different provider than the PW, an
operator may want to distinguish between defects detected in the ATM
access network and defects detected on the AC directly adjacent to
the PE. Therefore, the following option must also be supported:
a. PE1 MUST transparently relay ATM AIS cells over the
corresponding PW towards CE2.
b. Upon detection of a defect on the ATM interface on the
PE or in the PE itself, PE1 MUST send a forward defect
indication to PE2.
c. PE1 MUST cease generation of CC cells on the
corresponding PW, if applicable.
On exit from the AC receive defect state and when operating in the
"coupled OAM loops" mode:
a. PE1 MUST clear the forward defect indication to PE2.
b. PE1 MUST cease insertion of ATM RDI cells into the AC.
On exit from the AC receive defect state and when operating in the
"single emulated OAM loop" mode:
a. PE1 MUST cease insertion of ATM AIS cells into the
corresponding PW.
b. PE1 MUST clear the forward defect indication to PE2 if
applicable.
c. PE1 MUST resume any CC cell generation on the
corresponding PW, if applicable.
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9.3.5. AC transmit defect state entry/exit
On entry to the AC transmit defect state and when operating in the
"coupled OAM loops" mode:
a. PE1 MUST send a reverse defect indication to PE2.
On exit from the AC transmit defect state and when operating in the
"coupled OAM loops" mode:
a. PE1 MUST clear the reverse defect indication to PE2.
10. Procedures for Frame Relay PW Service
10.1. AC receive defect state entry/exit criteria
PE1 enters the AC receive defect state if one or more of the
following conditions are true:
a. A PVC is not deleted from the Frame Relay network and
the Frame Relay network explicitly indicates in a full
status report (and optionally by the asynchronous
status message) that this Frame Relay PVC is inactive
[ITU-T Q.933]. In this case, this status maps across
the PE to the corresponding PW only.
b. The Link Integrity Verification (LIV) indicates that
the link from the PE to the Frame Relay network is
down [ITU-T Q.933]. In this case, the link down
indication maps across the PE to all corresponding
PWs.
c. A physical layer alarm is detected on the FR
interface. In this case, this status maps across the
PE to all corresponding PWs.
PE1 exits the AC receive defect state when all defects it had
previously detected have disappeared.
10.2. AC transmit defect state entry/exit criteria
The AC transmit defect state is not valid for a FR AC.
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10.3. Consequent Actions
10.3.1. PW receive defect state entry/exit
On entry to the PW receive defect state:
a. PE1 MUST set the Active bit = 0 for the corresponding
FR AC in a full status report, and optionally in an
asynchronous status message, as per Q.933 annex A
[ITU-T Q.933].
b. If the PW failure was detected by PE1 without
receiving a forward defect indication from PE2, PE1
MUST assume PE2 has no knowledge of the defect and
MUST notify PE2 in the form of a reverse defect
indication.
On exit from the PW receive defect state:
a. PE1 MUST set the Active bit = 1 for the corresponding
FR AC in a full status report, and optionally in an
asynchronous status message, as per Q.933 annex A. PE1
does not apply this procedure on a transition from the
PW receive defect state to the PW transmit defect
state.
b. PE1 MUST clear the reverse defect indication to PE2 if
applicable.
10.3.2. PW transmit defect state entry/exit
On entry to the PW transmit defect state:
a. PE1 MUST set the Active bit = 0 for the corresponding
FR AC in a full status report, and optionally in an
asynchronous status message, as per Q.933 annex A.
b. If the PW failure was detected by PE1 without
receiving a reverse defect indication from PE2, PE1
MUST assume PE2 has no knowledge of the defect and
MUST notify PE2 in the form of a forward defect
indication.
On exit from the PW transmit defect state:
a. PE1 MUST set the Active bit = 1 for the corresponding
FR AC in a full status report, and optionally in an
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asynchronous status message, as per Q.933 annex A. PE1
does not apply this procedure on a transition from the
PW transmit defect state to the PW receive defect
state.
b. PE1 MUST clear the forward defect indication to PE2 if
applicable.
10.3.3. PW defect state in the FR Port Mode PW service
In case of port mode PW service, STATUS ENQUIRY and STATUS messages
are transported transparently over the PW. A PW Failure will
therefore result in timeouts of the Q.933 link and PVC management
protocol at the Frame Relay devices at one or both sites of the
emulated interface.
10.3.4. AC receive defect state entry/exit
On entry to the AC receive defect state:
a. PE1 MUST send a forward defect indication to PE2.
On exit from the AC receive defect state:
a. PE1 MUST clear the forward defect indication to PE2.
10.3.5. AC transmit defect state entry/exit
The AC transmit defect state is not valid for a FR AC.
11. Procedures for TDM PW Service
The following procedures apply to SAToP ([RFC4553]), CESoPSN
([RFC5086]) and TDMoIP ([RFC5087]). These technologies generally
utilize the single-emulated loop mode (see section 7). Note that
TDMoIP distinguishes between trail-extended and trail-terminated
scenarios; the former is essentially the single emulated loop model,
while the latter differs from the coupled-loop model in that failure
notifications are not propagated across the PW.
Since TDM is inherently real-time in nature, many OAM indications
must be generated or forwarded with essentially no delay. This
requirement rules out the use of messaging protocols, such as relying
on the PW status message. Thus, for TDM PWs, alternate mechanism are
employed.
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The fact that TDM PW packets are sent at a known constant rate is
used as an OAM mechanism. Thus, a PE enters the PW receive defect
state when a preconfigured number of TDM PW packets do not arrive in
a timely fashion. It exits this state when packets once again arrive
at the proper rate.
Native TDM carries OAM indications in overhead fields that travel
along with the data. TDM PWs emulate this behavior by sending urgent
OAM messages in the PWE control word.
The TDM PWE control word contains a set of flags used to indicate PW
and AC defect conditions. The L bit is an AC forward defect
indication used by the local PE to signal TDM network defects to the
remote PE. The M field may be used to modify the meaning of receive
defects. The R bit is a PW reverse defect indication used by the
local PE to signal PSN failures to the remote PE. Upon reception of
packets with the R-bit set, a PE enters the PW transmit defect state.
11.1. AC receive defect state entry/exit criteria
PE1 enters the AC receive defect state if any of the following
conditions are met:
e. It detects a physical layer fault on the TDM interface
(Loss of Signal, Loss of Alignment, etc (see G.705)).
f. It is notified of a previous physical layer fault by
detecting of AIS.
The exact conditions under which a PE enters and exits the AIS state
are defined in [ITU-T G.775]. Note that Loss of Signal and AIS
detection can be performed for both structure-agnostic and structure-
aware TDM PW types. Note that structure-agnostic PEs can not detect
Loss of Alignment.
11.2. AC transmit defect state entry/exit criteria
PE1 enters the AC transmit defect state when it detects RDI according
to the criteria in [ITU-T G.775]. Note that structure-agnostic PEs
can not detect RDI.
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11.3. Consequent Actions
11.3.1. PW receive defect state entry/exit
On entry to the PW receive defect state:
a. PE1 MUST commence AIS insertion into the corresponding
TDM AC.
b. PE1 MUST set the R bit in all PW packets sent back to
PE2.
On exit from the PW receive defect state:
c. PE1 MUST cease AIS insertion into the corresponding
TDM AC.
d. PE1 MUST clear the R bit in all PW packets sent back
to PE2.
Note that AIS generation can in general be performed by both
structure-aware and structure-agnostic PEs.
11.3.2. PW transmit defect state entry/exit
On entry to the PW Transmit Defect State:
a. A structure-aware PE1 MUST commence RDI insertion into
the corresponding AC.
On exit from the PW Transmit Defect State:
b. A structure-aware PE1 MUST cease RDI insertion into
the corresponding AC.
Note that structure-agnostic PEs are not capable of injecting RDI
into an AC.
11.3.3. AC receive defect state entry/exit
On entry to the AC receive defect state and when operating in the
"single emulated OAM loop" mode:
a. PE1 SHOULD overwrite the TDM data with AIS in the PW
packets sent towards PE2.
b. PE1 MUST set the L bit in these packets.
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c. PE1 MAY omit the payload in order to conserve
bandwidth.
d. A structure-aware PE1 SHOULD send RDI back towards
CE1.
e. A structure-aware PE1 that detects a potentially
correctable AC defect MAY use the M field to indicate
this.
On exit from the AC receive defect state and when operating in the
"single emulated OAM loop" mode:
a. PE1 MUST cease overwriting PW content with AIS and
return to forwarding valid TDM data in PW packets sent
towards PE2.
b. PE1 MUST clear the notification bit in PW packets sent
towards PE2.
c. A structure-aware PE1 MUST cease sending RDI towards
CE1.
12. Procedures for CEP PW Service
The following procedures apply to SONET/SDH Circuit Emulation
([RFC4842]). They are based on the single-emulated loop mode (see
section 7).
Since SONET and SDH are inherently real-time in nature, many OAM
indications must be generated or forwarded with essentially no delay.
This requirement rules out the use of messaging protocols, such as
relying on the PW status message. Thus, for CEP PWs alternate
mechanism are employed.
The CEP PWE control word contains a set of flags used to indicate PW
and AC defect conditions. The L bit is a forward defect indication
used by the local PE to signal a defect in the attachment circuit to
the remote PE. The R bit is a PW reverse defect indication used by
the local PE to signal PSN failures to the remote PE. The combination
of N and P bit is used by the local PE to signal loss of pointer to
the remote PE.
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The fact that CEP PW packets are sent at a known constant rate is
used as an OAM mechanism. Thus, a PE enters the PW receive defect
state it loses packet synchronization. It exits this state when it
regains packet synchronization. See [RFC4842] for further details.
12.1. Defect states
12.1.1. PW receive defect state entry/exit criteria
In addition to the conditions specified in section 8.2.1. PE1 will
enter the PW receive defect state if one of the following is true:
- it receives packets with the L bit set
- it receives packets with both the N and P bits set
- it loses packet synchronization
12.1.2. PW transmit defect state entry/exit criteria
In addition to the conditions specified in section 8.2.2. PE1 will
enter the PW transmit defect state if it receives packets with the R
bit set.
12.1.3. AC receive defect state entry/exit criteria
PE1 enters the AC receive defect state if any of the following
conditions are met:
a. It detects a physical layer fault on the TDM interface
(Loss of Signal, Loss of Alignment, etc (see
[appropriate SONET & SDH reference])).
b. It is notified of a previous physical layer fault by
detecting of AIS.
The exact conditions under which a PE enters and exits the AIS state
are defined in[ITU-T G.707] and [ITU-T G.806].
12.1.4. AC transmit defect state entry/exit criteria
The AC transmit defect state is not valid for CEP PWs. RDI signals
are forwarded transparently.
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12.2. Consequent actions
12.2.1. PW receive defect state entry/exit
On entry to the PW receive defect state:
a. PE1 MUST commence AIS-P/V insertion into the
corresponding AC.
b. PE1 MUST set the R bit in all PW packets sent back to
PE2.
On exit from the PW receive defect state:
a. PE1 MUST cease AIS-P/V insertion into the
corresponding AC.
b. PE1 MUST clear the R bit in all PW packets sent back
to PE2.
See [RFC4842] for further details.
12.2.2. PW transmit defect state entry/exit
On entry to the PW Transmit Defect State:
a. A structure-aware PE1 MUST commence RDI insertion into
the corresponding AC.
On exit from the PW Transmit Defect State:
a. A structure-aware PE1 MUST cease RDI insertion into
the corresponding AC.
12.2.3. AC receive defect state entry/exit
On entry to the AC receive defect state:
a. PE1 MUST set the L bit in these packets.
b. If Dynamic Bandwidth Allocation (DBA) has been
enabled, PE1 MAY omit the payload in order to conserve
bandwidth.
c. If Dynamic Bandwidth Allocation (DBA) is not enabled
PE1 SHOULD insert AIS-V/P in the SDH/SONET client
layer in the PW packets sent towards PE2.
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On exit from the AC receive defect state and when operating in the
"single emulated OAM loop" mode:
d. PE1 MUST cease overwriting PW content with AIS-P/V and
return to forwarding valid data in PW packets sent
towards PE2.
e. PE1 MUST clear the L bit in PW packets sent towards
PE2.
See [RFC4842] for further details.
13. Security Considerations
The mapping messages described in this document do not change the
security functions inherent in the actual messages.
14. IANA Considerations
There are none at this time.
15. References
15.1. Normative References
[BFD] Katz, D., Ward, D., "Bidirectional Forwarding Detection",
Internet Draft <draft-ietf-bfd-base-03.txt>, July 2005
[FRF.19] Frame Relay Forum, "Frame Relay Operations, Administration,
and Maintenance Implementation Agreement", March 2001
[ICMP] Postel, J. "Internet Control Message Protocol" RFC 792
[ITU-T G.707] Recommendation G.707 "Network Node Interface For The
Synchronous Digital Hierarchy", December 2003
[ITU-T G.775] Recommendation G.775 "Loss of Signal (LOS), Alarm
Indication Signal(AIS) and Remote Defect Indication (RDI) defect
detection and clearance criteria for PDH signals", October 1998
[ITU-T G.806] Recommendation G.806 "Characteristics of transport
equipment-Description methodology and generic functionality",
February 2004.
[ITU-T I.610] Recommendation I.610 "B-ISDN operation and maintenance
principles and functions", February 1999
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[ITU-T I.620] Recommendation I.620 "Frame relay operation and
maintenance principles and functions", October 1996
[ITU-T Q.933] Recommendation Q.933 "ISDN Digital Subscriber
Signalling System No. 1 (DSS1) Signalling specifications for
frame mode switched and permanent virtual connection control and
status monitoring" February 2003
[RFC3931] Lau, J., et. al. "Layer Two Tunneling Protocol (Version 3",
RFC 3931, March 2005
[RFC4023] Worster. T., et al., "Encapsulating MPLS in IP or Generic
Routing Encapsulation (GRE)", RFC 4023, March 2005
[RFC4379] Kompella, K., et. al., "Detecting MPLS Data Plane
Failures", RFC4379, February 2006
[RFC4447] Martini, L., Rosen, E., Smith, T., "Pseudowire Setup and
Maintenance using LDP", RFC4447, April 2006
[RFC4842] Malis, A., et. al., "SONET/SDH Circuit Emulation over
Packet (CEP)", RFC 4842, April 2007
[RFC5085] Nadeau, T., et al., "Pseudo Wire Virtual Circuit Connection
Verification (VCCV)", RFC 5085, December 2007
[VCCV-BFD] Nadeau, T., Pignataro, C., "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit Connectivity
Verification (VCCV)", draft-ietf-pwe3-vccv-bfd-02, June 2008
15.2. Informative References
[CONGESTION] Rosen, E., Bryant, S., Davie, B., "PWE3 Congestion
Control Framework", draft-ietf-pwe3-congestion-frmwk-01.txt, May
2008
[ETH-OAM-IWK] Mohan, D., et al., "MPLS and Ethernet OAM
Interworking", draft-mohan-pwe3-mpls-eth-oam-iwk-01, July 2008
[L2TP-Status] McGill, N. Pignataro, C., "L2TPv3 Extended Circuit
Status Values", draft-nmcgill-l2tpext-circuit-status-extensions-
01 (work in progress), June 2008.
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[RFC3916] Xiao, X., McPherson, D., Pate, P., "Requirements for
Pseudo Wire Emulation Edge to-Edge (PWE3)", RFC 3916, September
2004
[RFC3985] Bryant, S., Pate, P., "PWE3 Architecture", RFC 3985, March
2005
[RFC4377] Nadeau, T. et.al., "OAM Requirements for MPLS Networks",
RFC4377, February 2006
[RFC4446] Martini, L., et al., "IANA Allocations for pseudo
Wire Edge to Edge Emulation (PWE3)", RFC4446,
April 2006
[RFC4454] Singh, S., Townsley, M., and C. Pignataro, "Asynchronous
Transfer Mode (ATM) over Layer 2 Tunneling Protocol
Version 3 (L2TPv3)", RFC 4454, May 2006
[RFC4553] A.Vainshtein, Y.(J) Stein, "Structure-Agnostic Time
Division Multiplexing (TDM) over Packet (SAToP)", RFC 4553, June
2006
[RFC4717] Martini, L., et al., "Encapsulation Methods for Transport
of ATM Cells/Frame Over IP and MPLS Networks", RFC4717,
December 2006
[RFC5086] A.Vainshtein et al., "Structure-Aware Time Division
Multiplexed (TDM) Circuit Emulation Service over Packet Switched
Network (CESoPSN)", RFC 5086, December 2007
[RFC5087] Y.(J) Stein et al., "Time Division Multiplexing over IP
(TDMoIP)", RFC 5087, December 2007
16. Editor's Addresses
Mustapha Aissaoui
Alcatel-lucent
600 March Rd
Kanata, ON, Canada K2K 2E6
Email: mustapha.aissaoui@alcatel-lucent.com
Peter B. Busschbach
Alcatel-Lucent
67 Whippany Road
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Whippany, NJ, 07981
Email: busschbach@alcatel-lucent.com
David Allan
Nortel Networks
3500 Carling Ave.,
Ottawa, Ontario, CANADA
Email: dallan@nortel.com
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO, 80112
Email: lmartini@cisco.com
Thomas D. Nadeau
BT
BT Centre
81 Newgate Street
London EC1A 7AJ
United Kingdom
EMail: tom.nadeau@bt.com
Monique Morrow
Cisco Systems, Inc.
Glatt-com
CH-8301 Glattzentrum
Switzerland
EMail: mmorrow@cisco.com
Yaakov (Jonathan) Stein
RAD Data Communications
24 Raoul Wallenberg St., Bldg C
Tel Aviv 69719
ISRAEL
EMail: yaakov_s@rad.com
Informative Appendix A: Native Service Management
- Frame Relay Management
The management of Frame Relay Bearer Service (FRBS) connections can
be accomplished through two distinct methodologies:
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a. Based on ITU-T Q.933 Annex A, Link Integrity Verification
procedure, where STATUS and STATUS ENQUIRY signaling messages
are sent using DLCI=0 over a given UNI and NNI physical link.
[ITU-T Q.933]
b. Based on FRBS LMI, and similar to ATM ILMI where LMI is
common in private Frame Relay networks.
In addition, ITU-T I.620 addresses Frame Relay loopback, but the
deployment of this standard is relatively limited [ITU-T I.620].
It is possible to use either, or both, of the above options to
manage Frame Relay interfaces. This document will refer exclusively
to Q.933 messages.
The status of any provisioned Frame Relay PVC may be updated
through:
a. STATUS messages in response to STATUS ENQUIRY messages, these
are mandatory.
b. Optional unsolicited STATUS updates independent of STATUS
ENQUIRY (typically under the control of management system,
these updates can be sent periodically (continuous
monitoring) or only upon detection of specific defects based
on configuration.
In Frame Relay, a DLC is either up or down. There is no distinction
between different directions. To achieve commonality with other
technologies, down is represented as a receive defect.
Frame relay connection management is not implemented over the PW
using either of the techniques native to FR, therefore PW mechanisms
are used to synchronize the view each PE has of the remote NS/AC. A
PE will treat a remote NS/AC failure in the same way it would treat
a PW or PSN failure; that is using AC facing FR connection
management to notify the CE that FR is down.
- ATM Management
ATM management and OAM mechanisms are much more evolved than those
of Frame Relay. There are five broad management-related categories,
including fault management (FT), Performance management (PM),
configuration management (CM), Accounting management (AC), and
Security management (SM). ITU-T Recommendation I.610 describes the
functions for the operation and maintenance of the physical layer
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and the ATM layer, that is, management at the bit and cell levels
[ITU-T I.610]. Because of its scope, this document will concentrate
on ATM fault management functions. Fault management functions
include the following:
a. Alarm indication signal (AIS)
b. Remote Defect indication (RDI).
c. Continuity Check (CC).
d. Loopback (LB)
Some of the basic ATM fault management functions are described as
follows: Alarm indication signal (AIS) sends a message in the same
direction as that of the signal, to the effect that an error has
been detected.
Remote defect indication (RDI) sends a message to the transmitting
terminal that an error has been detected. RDI is also referred to as
the far-end reporting failure. Alarms related to the physical layer
are indicated using path AIS/RDI. Virtual path AIS/RDI and virtual
channel AIS/RDI are also generated for the ATM layer.
OAM cells (F4 and F5 cells) are used to instrument virtual paths and
virtual channels respectively with regard to their performance and
availability. OAM cells in the F4 and F5 flows are used for
monitoring a segment of the network and end-to-end monitoring. OAM
cells in F4 flows have the same VPI as that of the connection being
monitored. OAM cells in F5 flows have the same VPI and VCI as that
of the connection being monitored. The AIS and RDI messages of the
F4 and F5 flows are sent to the other network nodes via the VPC or
the VCC to which the message refers. The type of error and its
location can be indicated in the OAM cells. Continuity check is
another fault management function. To check whether a VCC that has
been idle for a period of time is still functioning, the network
elements can send continuity-check cells along that VCC.
Informative Appendix B: PW Defects and Detection tools
- PW Defects
Possible defects that impact PWs are the following:
a. Physical layer defect in the PSN interface
b. PSN tunnel failure which results in a loss of connectivity
between ingress and egress PE.
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c. Control session failures between ingress and egress PE
In case of an MPLS PSN and an MPLS-IP PSN there are additional
defects:
a. PW labeling error, which is due to a defect in the ingress
PE, or to an over-writing of the PW label value somewhere
along the LSP path.
b. LSP tunnel Label swapping errors or LSP tunnel label merging
errors in the MPLS network. This could result in the
termination of a PW at the wrong egress PE.
c. Unintended self-replication; e.g., due to loops or denial-
of-service attacks.
- Packet Loss
Persistent congestion in the PSN or in a PE could impact the proper
operation of the emulated service.
A PE can detect packet loss resulting from congestion through several
methods. If a PE uses the sequence number field in the PWE3 Control
Word for a specific Pseudo Wire [RFC3985], it has the ability to
detect packet loss. Translation of congestion detection to PW defect
states is outside the scope of this specification.
Generally, there are congestion alarms which are raised in the node
and to the management system when congestion occurs. The decision to
declare the PW Down and to select another path is usually at the
discretion of the network operator.
- PW Defect Detection Tools
To detect the defects listed above, Service Providers have a variety
of options available.
Physical Layer defect detection and notification mechanisms such as
SONET/SDH LOS, LOF, and AIS/FERF.
PSN Defect Detection Mechanisms:
For PWE3 over an L2TP-IP PSN, with L2TP as encapsulation protocol,
the defect detection mechanisms described in [RFC3931] apply. This
includes for example the keep-alive mechanism performed with Hello
messages for detection of loss of connectivity between a pair of
LCCEs (i.e., dead PE peer and path detection). Furthermore, the
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tools Ping and Traceroute, based on ICMP Echo Messages apply [RFC792]
and can be used to detect defects on the IP PSN. Additionally, ICMP
Ping [RFC5085] and BFD [VCCV-BFD] can also be used with VCCV to
detect defects at the individual pseudowire level.
For PWE3 over an MPLS PSN and an MPLS-IP PSN, several tools can be
used.
a. LSP-Ping and LSP-Traceroute( [RFC4379]) for LSP tunnel
connectivity verification.
b. LSP-Ping with Bi-directional Forwarding Detection ([BFD])
for LSP tunnel continuity checking.
c. Furthermore, if RSVP-TE is used to setup the PSN Tunnels
between ingress and egress PE, the hello protocol can be
used to detect loss of connectivity [RFC3209], but only at
the control plane.
PW specific defect detection mechanisms:
[RFC4377] describes how LSP-Ping and BFD can be used over individual
PWs for connectivity verification and continuity checking
respectively. When used as such, we will refer to them as VCCV-Ping
and VCCV-BFD respectively.
Furthermore, the detection of a fault could occur at different points
in the network and there are several ways the observing PE determines
a fault exists:
a. egress PE detection of failure (e.g. BFD)
b. ingress PE detection of failure (e.g. LSP-PING)
c. ingress PE notification of failure (e.g. RSVP Path-err)
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